The present invention relates to mobile vehicle packet data communication networks, and more particularly, to a mobile vehicle packet data communication network having multiple routing mode options and providing intelligent control thereof.
Mobile data networks can be classified into two major categories--circuit switched and packet switched. In circuit switched networks, an end-to-end "physical" connection is set up for the duration of the call and physical assets of the network are dedicated to the particular call for its duration. This does not preclude the case of call hand off, as performed in cellular networks, where the physical path may be switched during the call.
In packet data networks, an end-to-end connection is also set up for the duration of the call, but the connection is "logical", not physical. A logical connection merely establishes the routing of packets through a multiplicity of switching nodes within the network, the path being determined by source and destination addresses of the packets. It is not necessary to dedicate to the call a specific physical path for the entire call duration--packets with different source and destination addresses, following different logical paths, are time multiplexed on the links within the network.
Mobile packet data networks in existence today use exclusively a satellite transmission path or exclusively a terrestrial transmission path. An example of a commercial satellite packet data network is Inmarsat-C. An example of a commercial terrestrial packet data network is ARDIS. Cellular-type networks, including networks in both the common-carrier cellular bands and the Specialized Mobile Radio (SMR) bands, currently offer packet data services in addition to voice telephone services. Satellite transmission is characterized by large coverage footprints, whereas terrestrial mobile communication is usually of the cellular type and involves relatively small coverage cells with hand-off between cells.
Networks which are capable of using only one transmission medium or transmission path, such as a terrestrial transmission path or a satellite transmission path, require that tradeoffs be made between the advantages and disadvantages of each medium. For example, satellite transmission offers the advantage of wide coverage area owing to the large footprints of its beams. However, some of its major disadvantages are weak received signals, on the ground and at the satellite, and long transmission delays because of great propagation distances. In addition, satellite network infrastructure costs tend to be higher than their terrestrial counterparts.
In contrast, terrestrial transmission involves strong received signals, at the mobile terminal and at the base stations, and short delays owing to much shorter propagation distances. This simplifies receiver design and reduces mobile transmit power. In addition, the cost of terrestrial transmission, on a per mobile terminal basis, is typically lower than that of satellite transmission. It would be preferable for a packet data network to be able to take advantage of the best features of multiple transmission paths (i.e., of satellite and terrestrial transmission paths). However, no "multi-mode" packet data networks with this feature are believed to be available or to have been disclosed in the literature.
Disclosures have been made in the open literature regarding conceptual approaches for integrating "circuit-switched" mobile satellite communications and "circuit switched" cellular communications to provide "multi-mode" circuit switched communications. Thus, the advantages of both circuit switched satellite communication sub-networks and of circuit switched cellular communication sub-networks could in theory be combined. However, it is believed that no multi-mode circuit switched communication networks are commercially available. This is likely due, at least in part, to several difficult requirements that are inherent in multi-mode circuit switched networks.
All of the multi-mode systems discussed in the literature, relating to circuit switched networks, require direct connection between a terrestrial Mobile Telephone Switching Office (MTSO), also referred to as Mobile Switching Center (MSC), and a satellite base station, also referred to as satellite hub station (SHS). In other words, they require that a direct link be established between the two transmission path sub-networks which provide the multiple routing mode options. The direct link between the MTSO and the SHS is required for two reasons. First, because of the circuit switched nature of the application (voice telephony), a direct physical path must exist, end-to-end through the network, for the duration of the call. Second, because the public switched telephone networks (PSTN) cannot be modified easily, the mode switching must be performed outside the PSTN, such as in the MTSO and/or in the SHS. In other words, the switching must be performed inside of the two communication transmission path sub-networks--an undesirable requirement in most instances.
In addition to requiring a direct link between the MTSO and SHS sub-networks, modifications are required to the existing software of the MTSO and the SHS because the satellite and terrestrial transmission characteristics are sufficiently different that unmodified terrestrial hand off protocols cannot be used. These sub-network requirements and/or necessary modifications are undesirable and render many satellite and terrestrial sub-networks unusable as transmission paths in the circuit switched multi-mode communications networks described in the literature.
Consequently, a need exists for a multi-mode communication network which eliminates the undesirable requirements of the circuit switched multi-mode networks discussed in the literature, especially when circuit switching is not essential, while providing users with a wider coverage area, reduced costs, and a variety of data transmission rates and message delivery times. No disclosures have appeared in the open literature, nor are there any practical examples of, multi-mode packet switched networks.